1. Field of the Invention
This invention relates to a precision polishing apparatus for highly accurately polishing the surface or the like of a substrate such as a wafer on which dielectric material layers are laminated in a semiconductor device manufacturing process.
2. Related Background Art
In recent years, the tendency of semiconductor devices toward a high degree of minuteness has advanced and the accuracy of the order of submicrons has been required of the line width of minute patterns. Along with this, the technique of highly accurately flattening the surface of a substrate such as a wafer on which wiring or dielectric material layers are laminated has become necessary and a precision polishing apparatus adopting so-called mechano-chemical polishing or the like techniques in which a chemical reaction is effected on a polished surface has been developed.
Referring to FIG. 17 of the accompanying drawings which shows a precision polishing apparatus the inventor designed prior to the present invention, this apparatus has a substrate holder 1002 for adsorbing and holding a pair of wafers W.sub.0 in such a manner that the polished surfaces thereof face downward and conveying then along a guide 1001, loading portions 1003 disposed in series in the direction of conveyance of the wafers, a wafer centering portion 1004, a polishing portion 1005 for rotating a polishing pad 1005a on a stool, a wafer washing portion 1006, a wafer reversing portion 1007 and an unloading portion 1008.
Wafers W.sub.0 contained in a loading cassette G.sub.1 and carried in from the pre-process are taken out of the loading cassette G.sub.1 in the loading portion 1003, and are subjected to centering in the wafer centering portion 1004, whereafter they are adsorbed by the substrate holder 1002 and conveyed to the polishing portion 1005. In the polishing portion 1005, the substrate holder 1002 is made to cross along the diameter of the polishing pad 1005a while each wafer W.sub.0 is lightly urged against the surface of the polishing pad 1005a being rotated, thereby polishing the underside (the polished surface) of each wafer W.sub.0. The substrate holder 1002 which, as crossed the polishing pad 1005a is continuedly moved along the guide 1001 and arrives at the wafer washing portion 1006. Here, washing liquid is blown from a nozzle 1006a on to the polished surface of each wafer W.sub.0 to thereby remove the secondary product of polishing. The wafer reversing portion 1007 reverses the washed wafer W.sub.0 and transports it to the unloading portion 1008. In the unloading portion 1008, the water W.sub.0 is contained in an unloading cassette G.sub.2 and sent out to the next step.
The substrate holder 1002 is suspended from a top frame 1002a movable above the wafer centering portion 1004, the polishing portion 1005, the wafer washing portion 1006, etc., and one end of the top from 1002a is supported from reciprocal movement along the guide 1001 and the other end thereof is connected to a driving portion 1002b. The top frame 1002asuspended from the substrate holder 1002 is reciprocally moved along the guide 1001 by the driving of the driving portion 1002b. The polishing portion 1005 is provided with a brushing device 1005b and a hand shower 1005c for cleaning the surface of the polishing pad 1005a. As described above, the apparatus is designed such that the polishing of the wafers W.sub.0 continuously fed in from the pre-process and the subsequent washing step are automatically executed and the wafers are fed to the next step and the work of cleaning the surface of the polishing pad 1005a can be done efficiently which the substrate holder 1002 is moved in the opposite direction and returned from the unloading portion 1008 to the loading portion 1003.
According to the above-described technique, however, the series of steps of taking out the wafer carried in by a conveying device such as a conveyor out of the cassette, polishing the wafer and washing the polished surface thereof are automated to thereby greatly contribute to a reduction in the manufacturing cost of semiconductor devices or the like, but dust such as polishing powder created in the polishing portion enters the loading portion and the wafer washing portion adjoining the polishing portion and deteriorates the performance of the driving portion for these, and this leads to the problem of high cost which is left to be solved.
Also, an exposure apparatus or the like for wafer in the pre-process is generally operated under a cleaned atmosphere such as a clean room or the like and therefore, if the dust created in the polishing portion contaminates the atmosphere of the clean room, the performance of the exposure apparatus or the like may be remarkably spoiled. Further, is a great deal of polishing powder or the like enters the wafer washing portion together with the wafer taken out of the polishing portion, the quantity of washing liquid consumed will increase and the time spent for the washing of the wafer will also lengthen with a result that the manufacturing cost of semiconductor devices or the like will rise.